Webmaster level: all
A common annoyance for web users is when websites require browser technologies that are not supported by their device. When users access such pages, they may see nothing but a blank space or miss out a large portion of the page's contents.
Starting today in our English search results in the US, we will indicate to searchers when our algorithms detect pages that may not work on their devices. For example, Adobe Flash is not supported on iOS devices or on Android versions 4.1 and higher, and a page whose contents are mostly Flash may be noted like this:

This search label has been deprecated.

Developing modern multi-device websites

Fortunately, making websites that work on all modern devices is not that hard: websites can use HTML5 since it is universally supported, sometimes exclusively, by all devices. To help webmasters build websites that work on all types of devices regardless of the type of content they wish to serve, we recently announced two resources:

Web Starter Kit: a starter framework supporting the Web Fundamentals best practices out of the box.

By following the best practices described in Web Fundamentals you can build a responsive web design, which has long been Google's recommendation for search-friendly sites. Be sure not to block crawling of any Googlebot of the page assets (CSS, JavaScript, and images) using robots.txt or otherwise. Being able to access these external files fully helps our algorithms detect your site's responsive web design configuration and treat it appropriately. You can use the Fetch and render as Google feature in Webmaster Tools to test how our indexing algorithms see your site.
As always, if you need more help you can ask a question in our webmaster forum.Posted by Keita Oda, Software Engineer, and Pierre Far, Webmaster Trends Analyst